Download Spacecraft Onboard Interface Systems—Low Data

Recommendation for Space Data System Practices
SPACECRAFT ONBOARD INTERFACE
SYSTEMS—LOW DATA-RATE WIRELESS
COMMUNICATIONS FOR SPACECRAFT
MONITORING AND CONTROL
RECOMMENDED PRACTICE
CCSDS 882.0-M-1
MAGENTA BOOK
May 2013
RECOMMENDED PRACTICE FOR LOW DATA-RATE WIRELESS COMMUNICATIONS
AUTHORITY
Issue:
Recommended Practice, Issue 1
Date:
May 2013
Location:
Washington, DC, USA
This document has been approved for publication by the Management Council of the
Consultative Committee for Space Data Systems (CCSDS) and represents the consensus
technical agreement of the participating CCSDS Member Agencies. The procedure for
review and authorization of CCSDS documents is detailed in Organization and Processes for
the Consultative Committee for Space Data Systems (CCSDS A02.1-Y-3), and the record of
Agency participation in the authorization of this document can be obtained from the CCSDS
Secretariat at the address below.
This document is published and maintained by:
CCSDS Secretariat
Space Communications and Navigation Office, 7L70
Space Operations Mission Directorate
NASA Headquarters
Washington, DC 20546-0001, USA
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RECOMMENDED PRACTICE FOR LOW DATA-RATE WIRELESS COMMUNICATIONS
STATEMENT OF INTENT
The Consultative Committee for Space Data Systems (CCSDS) is an organization officially
established by the management of its members. The Committee meets periodically to address
data systems problems that are common to all participants, and to formulate sound technical
solutions to these problems. Inasmuch as participation in the CCSDS is completely
voluntary, the results of Committee actions are termed Recommendations and are not in
themselves considered binding on any Agency.
CCSDS Recommendations take two forms: Recommended Standards that are prescriptive
and are the formal vehicles by which CCSDS Agencies create the standards that specify how
elements of their space mission support infrastructure shall operate and interoperate with
others; and Recommended Practices that are more descriptive in nature and are intended to
provide general guidance about how to approach a particular problem associated with space
mission support. This Recommended Practice is issued by, and represents the consensus of,
the CCSDS members. Endorsement of this Recommended Practice is entirely voluntary
and does not imply a commitment by any Agency or organization to implement its
recommendations in a prescriptive sense.
No later than three years from its date of issuance, this Recommended Practice will be
reviewed by the CCSDS to determine whether it should: (1) remain in effect without change;
(2) be changed to reflect the impact of new technologies, new requirements, or new
directions; or (3) be retired or canceled.
In those instances when a new version of a Recommended Practice is issued, existing
CCSDS-related member Practices and implementations are not negated or deemed to be nonCCSDS compatible. It is the responsibility of each member to determine when such Practices
or implementations are to be modified. Each member is, however, strongly encouraged to
direct planning for its new Practices and implementations towards the later version of the
Recommended Practice.
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RECOMMENDED PRACTICE FOR LOW DATA-RATE WIRELESS COMMUNICATIONS
FOREWORD
This document is a CCSDS Recommended Practice, which is the consensus result as of the
date of publication of the Best Practices for low data-rate communication systems for
spacecraft monitor and control in support of space missions.
Through the process of normal evolution, it is expected that expansion, deletion, or
modification of this document may occur. This Recommended Practice is therefore subject
to CCSDS document management and change control procedures, which are defined in the
Organization and Processes for the Consultative Committee for Space Data Systems
(CCSDS A02.1-Y-3). Current versions of CCSDS documents are maintained at the CCSDS
Web site:
http://www.ccsds.org/
Questions relating to the contents or status of this document should be addressed to the
CCSDS Secretariat at the address indicated on page i.
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At time of publication, the active Member and Observer Agencies of the CCSDS were:
Member Agencies
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Agenzia Spaziale Italiana (ASI)/Italy.
Canadian Space Agency (CSA)/Canada.
Centre National d’Etudes Spatiales (CNES)/France.
China National Space Administration (CNSA)/People’s Republic of China.
Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)/Germany.
European Space Agency (ESA)/Europe.
Federal Space Agency (FSA)/Russian Federation.
Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
Japan Aerospace Exploration Agency (JAXA)/Japan.
National Aeronautics and Space Administration (NASA)/USA.
UK Space Agency/United Kingdom.
Observer Agencies
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Austrian Space Agency (ASA)/Austria.
Belgian Federal Science Policy Office (BFSPO)/Belgium.
Central Research Institute of Machine Building (TsNIIMash)/Russian Federation.
China Satellite Launch and Tracking Control General, Beijing Institute of Tracking
and Telecommunications Technology (CLTC/BITTT)/China.
Chinese Academy of Sciences (CAS)/China.
Chinese Academy of Space Technology (CAST)/China.
Commonwealth Scientific and Industrial Research Organization (CSIRO)/Australia.
CSIR Satellite Applications Centre (CSIR)/Republic of South Africa.
Danish National Space Center (DNSC)/Denmark.
Departamento de Ciência e Tecnologia Aeroespacial (DCTA)/Brazil.
European Organization for the Exploitation of Meteorological Satellites
(EUMETSAT)/Europe.
European Telecommunications Satellite Organization (EUTELSAT)/Europe.
Geo-Informatics and Space Technology Development Agency (GISTDA)/Thailand.
Hellenic National Space Committee (HNSC)/Greece.
Indian Space Research Organization (ISRO)/India.
Institute of Space Research (IKI)/Russian Federation.
KFKI Research Institute for Particle & Nuclear Physics (KFKI)/Hungary.
Korea Aerospace Research Institute (KARI)/Korea.
Ministry of Communications (MOC)/Israel.
National Institute of Information and Communications Technology (NICT)/Japan.
National Oceanic and Atmospheric Administration (NOAA)/USA.
National Space Agency of the Republic of Kazakhstan (NSARK)/Kazakhstan.
National Space Organization (NSPO)/Chinese Taipei.
Naval Center for Space Technology (NCST)/USA.
Scientific and Technological Research Council of Turkey (TUBITAK)/Turkey.
Space and Upper Atmosphere Research Commission (SUPARCO)/Pakistan.
Swedish Space Corporation (SSC)/Sweden.
United States Geological Survey (USGS)/USA.
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DOCUMENT CONTROL
Document
Title
Date
Status
CCSDS
882.0-M-1
Spacecraft Onboard Interface
Systems—Low Data-Rate Wireless
Communications for Spacecraft
Monitoring and Control,
Recommended Practice, Issue 1
May 2013
Current issue
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RECOMMENDED PRACTICE FOR LOW DATA-RATE WIRELESS COMMUNICATIONS
CONTENTS
Section
1
INTRODUCTION.......................................................................................................... 1-1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
2
PURPOSE ............................................................................................................... 1-1
SCOPE .................................................................................................................... 1-1
APPLICABILITY ................................................................................................... 1-1
RATIONALE.......................................................................................................... 1-1
DOCUMENT STRUCTURE ................................................................................. 1-1
DEFINITIONS........................................................................................................ 1-2
CONVENTIONS .................................................................................................... 1-2
REFERENCES ....................................................................................................... 1-3
OVERVIEW ................................................................................................................... 2-1
2.1
2.2
2.3
2.4
2.5
2.6
3
Page
RATIONALE AND BENEFITS ............................................................................ 2-1
SCOPE OF INTEROPERABILITY ....................................................................... 2-1
EVOLUTION OF THE BOOK .............................................................................. 2-2
DIFFERENTIATING CONTENTION-BASED AND
SCHEDULED CHANNEL ACCESS .................................................................... 2-3
SECURITY PROVISIONING ............................................................................... 2-4
QUALITY OF SERVICE PROVISIONING ......................................................... 2-4
RECOMMENDED PRACTICES FOR LOW DATA-RATE
WIRELESS COMMUNICATIONS FOR SPACECRAFT
MONITORING AND CONTROL ............................................................................... 3-1
3.1
3.2
OVERVIEW ........................................................................................................... 3-1
RECOMMENDED PRACTICES .......................................................................... 3-1
ANNEX A JUSTIFYING THE SCHEDULED MEDIUM ACCESS
RECOMMENDATION (INFORMATIVE) ............................................... A-1
ANNEX B SECURITY CONCERNS FOR WIRELESS SYSTEMS
(INFORMATIVE) ..........................................................................................B-1
ANNEX C DISCUSSION ON LOW DATA-RATE WIRELESS
COMMUNICATIONS FOR SPACECRAFT MONITORING
AND CONTROL (INFORMATIVE).......................................................... C-1
ANNEX D JUSTIFICATIONS FOR THE 2.4 GHZ BAND PREFERENCE
(INFORMATIVE) ......................................................................................... D-1
ANNEX E ABBREVIATIONS AND ACRONYMS (INFORMATIVE).....................E-1
ANNEX F INFORMATIVE REFERENCES (INFORMATIVE) ............................... F-1
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CONTENTS (continued)
Figure
Page
2-1 IEEE 802.15.4 Superframe ........................................................................................... 2-5
Table
2-1 PHY/MAC Security Service Provisioning ................................................................... 2-4
C-1 Application Profile Quick Look-Up Table ...................................................................C-4
C-2 Quick-Look Table for Scenarios That Can Utilize Low Data-Rate Wireless
Communications ...........................................................................................................C-4
C-3 Typical Operating Parameters for the Single-Hop, Periodic Data Aggregation
Application Profile ........................................................................................................C-6
C-4 Typical Operating Parameters for the Single-Hop Triggered, Event-Driven Data
Acquisition Application Profile ....................................................................................C-7
C-5 Typical Operating Parameters for the Single-Hop Command and Control Application
Profile............................................................................................................................C-9
D-1 Power Regulations ....................................................................................................... D-2
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1
1.1
INTRODUCTION
PURPOSE
This document presents the recommended practices for the utilization of low data-rate
wireless communication technologies in support of spacecraft ground testing and flight
monitoring and control applications. Relevant technical background information can be
found in reference [3].
The recommended practices contained in this document enable member agencies to select the
best option(s) available for interoperable wireless communications in the support of
spacecraft monitoring and control applications. The specification of a Recommended
Practice facilitates interoperable communications and forms the foundation for cross-support
of communication systems between separate member space agencies.
1.2
SCOPE
This Recommended Practice is targeted towards monitoring and control systems, typically
low data-rate and low-power wireless-based applications.
1.3
APPLICABILITY
This Recommended Practice specifies protocols (including at least the Physical [PHY] layer
and Medium Access Control [MAC] sublayer of the Open Systems Interconnection [OSI]
Model—see reference [F1]) that enable a basic interoperable wireless communication system
to support low data-rate spacecraft monitoring and control applications.
1.4
RATIONALE
From an engineering standpoint, mission managers, along with engineers and developers, are
faced with a plethora of wireless communication choices, both standards-based and
proprietary. This Recommended Practice provides guidance in the selection of systems
necessary to achieve interoperable communications in support of wireless, low data-rate
monitoring and control.
1.5
DOCUMENT STRUCTURE
This document is composed from a top-down (technology) perspective, first defining the
technology as a recommended practice, then providing informative material supporting specific
application profiles. (For more information on space mission use cases addressed by wireless
technologies, see reference [3]).
Section 2 provides an informational overview of the rationale and benefits of spacecraft
onboard wireless technologies for use in spacecraft monitoring and control operations.
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Section 3 provides recommended practices and applicable standards relating to low data-rate
wireless communication systems.
Annex A justifies the choice of an alternative, scheduled medium access scheme.
Annex B discusses security considerations related to the specifications in this document.
Annex C provides an informative description of the recommended practices, through an
overview of the technologies, and a set of application profiles where the recommendations
are applicable.
Annex D provides justification for selection of the 2.4 GHz band.
Annex E lists abbreviations used in this document along with their expanded forms.
Annex F provides a list of informative references.
1.6
DEFINITIONS
low data-rate: 250 kbps or less.
NOTE – In general the definition of low data-rate is somewhat ambiguous; for this
Recommended Practice it is specified as 250 kbps.
low power: 10 mW or less (typical).
quality of service, QoS: The ability to provide different priority to different applications,
users, or data flows, or to guarantee a certain level of performance to a data flow.
1.7
CONVENTIONS
1.7.1 NOMENCLATURE
The following conventions apply for the normative specifications in this Recommended
Practice:
a) the words ‘shall’ and ‘must’ imply a binding and verifiable specification;
b) the word ‘should’ implies an optional, but desirable, specification;
c) the word ‘may’ implies an optional specification;
d) the words ‘is’, ‘are’, and ‘will’ imply statements of fact.
NOTE – These conventions do not imply constraints on diction in text that is clearly
informative in nature.
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1.7.2 INFORMATIVE TEXT
In the normative section of this document, informative text is set off from the normative
specifications either in notes or under one of the following subsection headings:
1.8
–
Overview;
–
Background;
–
Rationale;
–
Discussion.
REFERENCES
The following publications contain provisions, which through reference in this text,
constitute provisions of this document. At the time of publication, the editions indicated
were valid. All publications are subject to revision, and users of this document are
encouraged to investigate the possibility of applying the most recent editions of the
publications indicated below. The CCSDS Secretariat maintains a register of currently valid
CCSDS publications.
[1]
IEEE Standard for Local and Metropolitan Area Networks—Part 15.4: Low-Rate
Wireless Personal Area Networks (LR-WPANs). IEEE Std 802.15.4a™-2011. New
York: IEEE, 2011.
[2]
Wireless Systems for Industrial Automation: Process Control and Related Applications.
ISA-100.11a-2011. Durham, North Carolina: ISA, 2011.
[3]
Wireless Network Communications Overview for Space Mission Operations. Report
Concerning Space Data System Standards, CCSDS 880.0-G-1. Green Book. Issue 1.
Washington, D.C.: CCSDS, December 2010.
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2
2.1
OVERVIEW
RATIONALE AND BENEFITS
Monitoring and controlling the behavior of a spacecraft and launch systems, during testing
phases on ground or during nominal operations in orbit, is the key to ensuring the correct
functioning of various onboard systems and structures, the responses of these systems in their
operational working environments, and the long-term reliability of the spacecraft. These data
are also highly significant when compiling lessons learned that will be applied to building
better space systems and increasing the reliability of future space components. (Refer to
reference [3] for a comprehensive overview of application domains and for a detailed
summary of RF communications and restrictions in differing operational environments.)
The quantity of acquired spacecraft functional data depends on the ability to monitor required
parameters at precise locations within a given project time and cost envelope. Hundreds and
often thousands of data measurement locations are required, steadily increasing the mass
(acquisition systems, cables, and harnesses) and the project costs and time (installation and
verification of each new sensor).
The use of wireless technologies is foreseen to reduce the integration effort, cost, and time
typically required to instrument a high number of physical measurement points on a space
structure. Technicians should need less time to integrate and verify their installations, while
the risk of mechanically damaging interfaces during the process should be reduced. Large
structures should see health monitoring equipment mass reduced, while last-minute changes
in the instrumentation (e.g., addition/removal of sensing nodes at measurement points)
should be easier to accept at project level. One of the byproducts of using wireless
technologies in space systems is the extra flexibility introduced when implementing wireless
fault-tolerance and redundancy schemes.
An overriding consideration in this document is the desire to provide recommendations that
utilize wireless technology to augment the overall networking infrastructure in a spacecraft
rather than to provide dedicated data transport to particular end-to-end application-specific
subsystems. That is, although the recommendations specified in this document are related to
relatively small-scale Personal Area Networks (PANs) rather the more familiar Local Area
Networks (LANs) such as Ethernet, the desire is for wireless PANs to function as natural
extensions of the backbone LAN. This implies in particular that the recommendations
specified herein focus on providing wireless data transport across the lower levels of the OSI
model (PHY and MAC) and not on achieving higher-level application-specific behavior.
2.2
SCOPE OF INTEROPERABILITY
The intent of the recommended practices promulgated in this book is to provide a framework
for establishing a scalable wireless infrastructure for low-rate data transport that will (1)
support traffic generated by diverse sensor types, multiple application-specific devices, and
devices supplied by multiple different vendors and (2) facilitate operation of multiple
wireless networks in the same bandwidth with minimal interference. The recommended
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practices will ensure interoperability of low data-rate wireless devices on a common network
at the PHY layer and MAC sublayer so that data packets generated by new devices entering
the network will be transported by the existing network devices without regard to the sensor
or application that generated the data in the packet payload. In its current form, the book’s
recommendations should allow new nodes to enter a star topology network and begin
communicating with a gateway. Should future revisions augment the current
recommendations to allow for transport mechanisms such as peer-to-peer communication and
multi-hop relaying, new nodes entering the network will not only be able to transmit their
own data to a gateway, but they may also be able to communicate with other nodes and to
transport data for other network devices.
Adherence to these recommended practices will promote interoperability of the low data-rate
wireless networks addressed in this document with other wireless networks using the same
bandwidth via the interference mitigation techniques encompassed by the recommendations.
2.3
EVOLUTION OF THE BOOK
The current version of this document specifies two recommended practices for low data-rate
spacecraft monitoring and control. Functionally, the current recommendations can be
regarded as pertaining only to the behavior of the network at the PHY layer and MAC
sublayer of the OSI network stack, not at the Logical Link sublayer or higher. This level of
detail in the recommendations is in line with the philosophy discussed in 2.1 above, that the
recommended behavior of wireless networks should be specified only at the lower layers of
the network stack (similar to the behavior specified for the backbone network in the
spacecraft), leaving higher-layer behavior at the discretion of system designers.
Furthermore, the two recommended practices specified in the current version of the
document are restricted to a subset of the network functionality generally supported by the
PHY and MAC layers of the OSI stack: one for single-hop contention-based access within a
star topology and one for single-hop scheduled access within a star topology. Hence, both
recommendations provide a mechanism for data packets to be exchanged between a network
coordinator or gateway and individual nodes on the wireless network, but they do not address
a mechanism for data packets to be exchanged between two non-coordinator nodes in the
network or for communication between any two nodes via intermediary nodes in a multi-hop
fashion. The evolution of this document is foreseen to propose additional recommended
practices for anticipated application profiles, such as recommended practices for peer-to-peer
communication in both mesh and star topologies and for multi-hop data transport in mesh
topologies.
The current recommendations also do not address a mechanism for exchanging data packets
between a node on the network and a device outside of the wireless network. It is assumed
that the network coordinator or gateway will somehow be able to communicate with the
backbone network of the spacecraft, but the mechanisms for that, which are typically
implemented at the Network (NWK) Layer of the stack, are beyond the scope of the current
document and are not discussed. Similarly, the recommendations do not discuss or provide
mechanisms for end-to-end acknowledgement or re-transmission of data packets sent
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between user applications. The mechanisms for that behavior are typically implemented at
the Transport or the Application (APP) Layer of the stack and once again are beyond the
scope of the current document. While it is anticipated that future recommendations may
address some functionality at the NWK layer, such as routing of Internet Protocol (IP)
packets within the wireless network, it is not anticipated that protocol behavior above the
NWK layer (such as any APP-layer functionality) will be addressed by future
recommendations.
2.4
DIFFERENTIATING CONTENTION-BASED AND SCHEDULED CHANNEL
ACCESS
There are two predominant types of medium-access schemes currently utilized in wireless
sensor networks: random or contention-based access and scheduled access (see
reference [F2]). Contention-based schemes require no centralized control of network access
and are thus well suited for ad-hoc network architectures as well as other situations where it
is desirable to minimize network administration overhead and operational complexity. Nodes
are allowed to attempt channel access at arbitrary times in an ad-hoc fashion as dictated by
local data traffic flow and must therefore contend with one another for access in a fairly
random manner. The most common contention-based access technique utilized in sensor
networks is Carrier-Sense Multiple Access (CSMA) with Collision Avoidance (CA),
generally abbreviated as CSMA-CA or simply CSMA. In contrast, scheduled access schemes
require some type of (generally centralized) control mechanism for coordinating network
access for all nodes in the network in a synchronized fashion. Typically, this will be based on
predetermined or anticipated traffic flow so that bandwidth is available in a predictable
manner that precludes contention among the nodes. This approach increases network
administrative overhead and operational complexity but facilitates QoS guarantees and
deterministic network behavior. The most common scheduled access technique utilized in
sensor networks is Time-Division Multiple Access (TDMA).
In terms of application support, CSMA is best suited for situations where tight bounds on
packet latency and packet jitter are not required but nodes may sometimes require relatively
large amounts of available channel bandwidth for relatively short periods of time in a
relatively unpredictable manner. CSMA does not readily support deterministic network
behavior but does readily support bursty and aperiodic traffic flow. In contrast, TDMA is
well suited for applications requiring much tighter bounds on packet latency and jitter but for
which the traffic flow from the nodes is more uniform and predictable. TDMA readily
supports deterministic network behavior but is generally better suited for applications with
less bursty and more periodic traffic flow. In addition, interference avoidance schemes such
as frequency hopping are far more easily implemented in a scheduled TDMA MAC sublayer
than in a contention-based CSMA MAC sublayer. The same applies to maintaining
connectivity in a mesh network topology that supports multi-hop relay traffic with battery
powered nodes on a low duty cycle (long sleep period, short active period), although multihop transport is beyond the scope of the current Recommended Practice.
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2.5
SECURITY PROVISIONING
Wireless networks suffer the maladies of both active tampering and passive eavesdropping
due to the inherent nature of wireless communications where access to the transmission
media is not a physical constraint as within wired communications. In addition, wireless
sensors have severely limited computational processing power and may have no available
onboard data storage. Because of the computational complexity of cryptographic algorithms,
coupled with the limited battery-based lifetime of a wireless sensor node, security
provisioning in these types of devices is a pragmatic engineering balance.
The cryptographic mechanism in this standard is based on symmetric-key cryptography and
uses keys that are provided by higher-layer processes; the mechanism assumes a secure
implementation of cryptographic operations and secure and authentic storage of keying
material (reference [1]). For the recommended practice contained in this document, the
PHY/MAC layer provides services that support data confidentiality, data integrity
(authenticity), and replay protection:
Table 2-1: PHY/MAC Security Service Provisioning
Security service
Description
Data confidentiality
Transmitted information is disclosed only to
parties for which it is intended
Data integrity
Assurance of the source of transmitted
information (and, hereby, that information
was not modified in transit)
Replay protection
Assurance that duplicate information is
detected
NOTE – Per annex B some of the required security architectural elements may be
implemented at higher layers (e.g., key management) in the OSI stack and are not
strictly defined, or implemented, at the PHY/MAC layer.
2.6
QUALITY OF SERVICE PROVISIONING
Both of the recommended practices prescribed in 3.2 provide support for implementing QoS
provisioning so that system designers can implement their QoS policies over the wireless
network.
In the 802.15.4 CSMA-CA operational mode, QoS primitive operations are achieved
utilizing Guaranteed Time Slots (GTS) as shown in figure 2-1. Briefly, the active portion of
the superframe is composed of a beaconing period, a Contention Access Period (CAP) and a
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Contention Free Period (CFP); the slotted CSMA scheme is utilized during the CAP, and the
GTS scheme is utilized during the CFP period.
Beacon
Active portion
Inactive portion
Beacon
CFP
CAP
GTS
GTS
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
superframe duration
beacon interval
Figure 2-1: IEEE 802.15.4 Superframe
The GTS scheme enables bandwidth reservation between an 802.15.4 PAN coordinator and a
PAN device. Notably, more sophisticated QoS schemes that attempt to enforce either some
type of fairness for all nodes in the network and/or to handle nodes entering and leaving the
network are advanced functionality that is typically implemented at the higher Network
(NWK) Layer of the communications stack.
In the 802.15.4 scheduled medium-access operational mode, which is TDMA-based, the
available TDMA slots are analogous to CSMA GTS slots during the CFP. Integrated
communication stacks based on 802.15.4 (e.g., ZigBee, ISA100, 6LoWPAN, 802.15.4e—see
reference [F7]) all enable deployment-wide QoS at the NWK layer. (Refer to annex A for
additional QoS provisioning provided in the ISA100.11a recommendation.)
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3
3.1
RECOMMENDED PRACTICES FOR LOW DATA-RATE
WIRELESS COMMUNICATIONS FOR SPACECRAFT
MONITORING AND CONTROL
OVERVIEW
This section presents the recommended practices for spacecraft monitoring and control
applications using low data-rate wireless communication technologies. (See table C-2 for a
non-exhaustive set of example use-cases that may benefit from using low data-rate wireless
communications.)
As discussed in section 2, in order to ensure the most basic interoperability between low
data-rate wireless communication devices, the current recommendations are focused on
specification of functionality at the air interface PHY layer and the MAC sublayer of the OSI
model. Following this guideline, two different compliant systems would thus be able to share
the medium and potentially join the same wireless network.
3.2
RECOMMENDED PRACTICES
3.2.1 APPLICATIONS SUITED FOR SINGLE-HOP CONTENTION-BASED
COMMUNICATIONS
For spacecraft monitoring and control activities employing low data-rate contention-based
wireless communications in single-hop configurations, both the air interface PHY layer and
the MAC sublayer shall comply with the IEEE 802.15.4-2011 specification (reference [1]).
Single-hop contention-based communication networks and devices should utilize the 2.4
GHz frequency band. (See annex D for rationale pertaining to 2.4 GHz band preferences; see
reference [3] for Electromagnetic Interference (EMI) considerations of the 2.4 GHz
frequency band.)
3.2.2 APPLICATIONS SUITED FOR SINGLE-HOP SCHEDULED MEDIUMACCESS COMMUNICATIONS
For spacecraft monitoring and control activities employing low data-rate communications
utilizing a scheduled medium-access scheme in a single-hop configuration, both the air
interface PHY layer and the MAC sublayer shall comply with the ISA100.11a-2011 PHYlayer and MAC-sublayer specifications (reference [2]).
3.2.3 RESTRICTIONS/HAZARDS
When selecting a wireless technology for application in a spacecraft environment, the risks
associated with the selected radio frequency band, transmission power level, and physical
location should be taken into account for the following governing environmental factors:
a) Operation in explosive environments;
b) RF exposure levels in excess of governmental limits (see annex D);
c) Electromagnetic Compatibility (EMC).
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ANNEX A
JUSTIFYING THE SCHEDULED MEDIUM ACCESS
RECOMMENDATION
(INFORMATIVE)
A1
BACKGROUND
From its introduction 2003, application of IEEE 802.15.4 to embedded sensing tasks has
been steadily increasing. Use has been largely limited to home and office automation,
however, since it has been found that 802.15.4 reliability suffers as the RF complexity of the
environment in which it is deployed increases. Specifically, industrial deployments of
802.15.4 are often observed to exhibit unacceptably low reliability and high latencies.
Amendments incorporated in the IEEE 802.15.4-2006 revision recommended, and even those
subsequently incorporated in the 802.15.4-2011 revision, have failed to address these
concerns adequately, leading to native IEEE 802.15.4’s being widely considered a poor
solution for process monitoring and control in harsh industrial environments.
This discrepancy is documented in the IEEE 802.15.4e-2012 amendment, which incorporates
a scheduled MAC layer very similar to the ISA100.11a MAC recommended in this Magenta
Book. In justifying the update to 802.15.4-2011 provided by the 802.15.4e amendment, the
IEEE states that “this amendment to IEEE Std 802.15.4-2011 specifies additional media
access control (MAC) behaviors and frame formats that allow IEEE 802.15.4 devices to
support a wide range of industrial and commercial applications that were not adequately
supported prior to the release of this amendment.”
It goes on to observe “industrial
applications (and some commercial applications) have critical requirements such as low
latency, robustness in the harsh industrial RF environment, and determinism that are not
adequately addressed by IEEE Std 802.15.4-2011” (reference [F7]).
Given that many spaceflight applications have constraints on reliability and latency similar to
those in industrial process control, it was determined that this Magenta Book required a
recommendation that rectifies many of the shortcomings in IEEE 802.15.4-2006 (and later,
802.15.4-2011) that the IEEE itself recognizes. Unfortunately, IEEE 802.14.4e-2012 is new
enough that there are not sufficient commercial parts available for testing to justify its
inclusion in the present edition of this Magenta book, although future editions may adopt it as
the scheduled MAC recommendation.
Instead, the ISA100.11a MAC, which along with the WirelessHART standard inspired the
IEEE 802.15.4e-2012 recommendation, is adopted here due to the availability of radios for
testing. Indeed, testing by the authors of this Magenta Book has confirmed the relative
robustness of ISA100.11a and the relative weakness of IEEE 802.15.4 in the presence of WiFi interference (reference [F8]). ISA100.11a is chosen over WirelessHART since it is
capable of supporting a greater variety of application layers and is in general more
customizable. (For a detailed comparison of the two, see reference [F9].)
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A2
MECHANISMS FOR INCREASED ROBUSTNESS
ISA100.11a provides a number of mechanisms for increasing the overall quality of service.
As mentioned in 2.4, the scheduled ISA100.11a MAC provides greater determinism for
channel access. Time in an ISA100.11a network is divided into slots, and a time distribution
mechanism embedded in packet acknowledgements ensures that radios keep slot boundaries
synchronized with respect to neighboring radios to ensure coordinated transmission/reception
between communicating pairs.
A Network Manager overseeing operation of the ISA100.11a network allocates
communication opportunities to radios requesting bandwidth, thereby ensuring time diversity
within the ISA100.11a network. That is, an individual radio within the network will only
attempt to use the wireless medium in a time slot assigned to that radio for transmission. If
the attempt fails for any reason (e.g., excessive RF interference), the transmission will be
retried at the radio’s next scheduled opportunity. Furthermore, frequency diversity is added
by the Network Manager, assigning one of the up to 16 channels available under the 802.15.4
2.4 GHz DSSS PHY employed by ISA100.11a to the communication attempt. Should a
retransmission be required, the next scheduled attempt will be on a different channel, drawn
from a predetermined channel-hopping sequence. Time synchronization between radios
allows the Network Manager to configure the receiving radio to have its receiver tuned to the
channel of the transmitter for the scheduled transaction. ISA100.11a supports adaptive
blacklisting, so that channels on which communication attempts repeatedly fail can be
removed from sending and receiving radios’ channel hopping sequences. For multi-hop
topologies, spatial diversity is also added through the use of routing graphs with redundant
next-hop paths, although that is outside the scope of this Magenta Book’s current
recommendation for single-hop communication.
These diversity features, taken together, enhance the ability of ISA100.11a to coexist with
other RF systems that are acting as interferers. It should also be noted that, since ISA100.11a
uses the 2.4 GHz DSSS PHY specified in IEEE 802.15.4-2006, it inherits the benefits of the
Clear Channel Assessment (CCA) service used by the CSMA MAC of 802.15.4, which in
particular promotes non-interference of the ISA100.11a radios with other systems operating
in the same RF band.
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ANNEX B
SECURITY CONCERNS FOR WIRELESS SYSTEMS
(INFORMATIVE)
B1
INTRODUCTION
The 802.15.4 and ISA100.11a specifications recommended in this book describes RF
wireless PHY-layer and MAC-sublayer protocols for low-power and relatively low data-rate
networked communications. These specifications support a diverse application domain;
wireless applications for space operations can benefit from the security features provided in
these PHY-layer/MAC-sublayer protocol specifications.
Communications security attempts to ensure the confidentiality, integrity, and/or authenticity
of transmitted data, as required depending on the threat, the mission security policy(s), and
the desire of the mission planners. It is possible, and often likely, to require all three of these
security attributes to ensure that the communications data payload is not disclosed, not
altered, and not spoofed.
Specific potential threats and attack scenarios relevant to the space flight operations domain
are addressed in more detail in reference [F5]. A summary of typical space agency use cases
is provided in reference [3]. Threats and attack scenarios for ground segment operations, i.e.,
AIT activities, are typical in scope to general terrestrial security concerns.
B2
GENERAL RISKS
A MAC-sublayer security protocol provides four basic security services: access control,
message integrity, message confidentiality, and replay protection (reference [F6]).
Access control and message integrity. Access control means the MAC-sublayer protocol
should prevent unauthorized parties from participating in the network. Legitimate nodes
should be able to detect messages from unauthorized nodes and reject them. Also, a secure
network should provide message integrity protection: if an adversary modifies a message
from an authorized sender while the message is in transit, the receiver should be able to
detect this tampering. Including a message authentication code with each packet provides
message authentication and integrity (reference [F6]).
Confidentiality. Confidentiality means keeping information secret from unauthorized parties.
It is typically achieved with encryption. Preferably, an encryption scheme should not only
prevent message recovery, but also prevent adversaries from learning even partial
information about the messages that have been encrypted (reference [F6]).
Replay Protection. An adversary that eavesdrops on a legitimate message sent between two
authorized nodes and replays it at some later time engages in a replay attack. Since the
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message originated from an authorized sender it will have a valid message authentication
code, so the receiver will accept it again. Replay protection prevents these types of attacks
(reference [F6]).
The 802.15.4 security implementation is handled at the MAC sublayer, below application
control. The application specifies its security requirements by setting the appropriate control
parameters in the radio stack. If an application does not set any parameters, then security is
not enabled by default. That is, when using 802.15.4, an application must explicitly enable
security. As discussed in C1.3, security is implemented automatically in ISA100.11a.
B3
SECURITY CONCERNS
Several security concerns specific to the IEEE 802.15.4 design are addressed in more detail
in reference [F6]; the reader is strongly encouraged to review the identified shortcomings. It
may be necessary to apply security services at multiple layers within the protocol stack, to
account for distributed processing and cross-support, to account for different classes of data
or end users, or to account for protection of data during unprotected portions of the complete
end-to-end transmission (e.g., across ground networks). The specification of security services
at other layers is outside the scope of this document.
B4
CONSEQUENCES OF NOT APPLYING SECURITY
Without authentication, unauthorized commands or software might be uploaded to a
spacecraft or data received from a source masquerading as the spacecraft. Without data
integrity, corrupted commands or software might be uploaded to a spacecraft potentially
resulting in the loss of the mission. Without data integrity, corrupted telemetry might be
retrieved from a spacecraft that could result in an incorrect course of action being taken. If
confidentiality is not implemented, data flowing to or from a spacecraft might be visible to
unauthorized entities resulting in disclosure of sensitive or private information.
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ANNEX C
DISCUSSION ON LOW DATA-RATE
WIRELESS COMMUNICATIONS FOR
SPACECRAFT MONITORING AND CONTROL
(INFORMATIVE)
C1
C1.1
GENERAL
OVERVIEW
The following subsections contain engineering discussions applicable to the recommended
practices in section 3.
C1.2
CONTENTION-BASED CHANNEL-ACCESS MECHANISM
As discussed in 2.4, the operation of a contention-based channel-access mechanism cannot
readily support packet delivery with reliably low and predictable latency in many situations,
particularly when the number of active nodes in the network grows to even moderate levels.
As such, it is generally not appropriate for use in situations requiring deterministic or ‘realtime’ behavior, such as spacecraft control guidance and navigation loops or life-critical
applications.
Similarly, the 802.15.4 MAC sublayer specified in Recommended Practice 3.2.1 provides no
specific mechanisms for adaptive channel selection or interference avoidance. The
recommendation as stated presumes operation on a single, predetermined subchannel of the
2.4 GHz ISM band and persistent interference on the selected channel will lead to substantial
performance degradation. Mechanisms for detecting and avoiding such interference, if
necessary, must be implemented at higher layers of the protocol stack. As such, the current
recommended practice may not be well suited for operation in a very cluttered spectral
environment with many different wireless systems contending for the same bandwidth.
Additionally, the environment may induce interference effects such as multi-path fading.
When these effects are time-varying and not well characterized a priori, the current
recommended practice may not be well suited. Conversely, the current recommended
practice can be expected to work very well in environments for which the available spectrum
is well understood over time and carefully managed..
Although Recommended Practice 3.2.1 applies specifically only to single-hop
communication between a client node and the network coordinator in a star network
topology, the recommended standard protocol, IEEE 802.15.4, will also support
communication modes and services not specifically addressed in the recommendation if
appropriate functionality is provided by higher layers of the protocol stack. For example,
while considerations regarding communication security are beyond the scope of the current
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recommendation, the 802.15.4 MAC sublayer specification defines encryption and
decryption services for symmetric-key cryptographic techniques that will support secure
communication if procedures for establishing and maintaining the necessary keys are
provided by higher layers. Similarly, while peer-to-peer and multi-hop communication within
an arbitrary mesh topology are beyond the scope of the current recommendation, the
802.15.4 MAC sublayer specification does provide support for these communication modes
if the necessary routing and synchronization mechanisms are implemented in higher layers of
the protocol stack.
These limitations and capabilities must be understood and considered carefully when making
an engineering decision regarding the applicability of a contention-based access mechanism
in general or recommendation 3.2.1 in particular.
C1.3
SCHEDULED CHANNEL-ACCESS MECHANISM
A scheduled channel-access mechanism requires a method for synchronizing
transmissions/receptions among the nodes in the network. Furthermore, the ISA100.11a
recommendation allows nodes to switch among the 16 available channels in the 802.15.4 2.4
GHz PHY with each subsequent transmission attempt, coordinating transmitters and
receivers so that they both use the same channel at the same time. As discussed in annex A, a
centralized Network Manager entity is required to establish this ‘channel hopping’
mechanism for each node in the network and mediate bandwidth usage through granting
communication ‘contracts’ to nodes.
The Network Manager is the key to an ISA100.11a network’s operation and is its most
complicated component. A Network Manager is constantly optimizing the channel-hopping
scheme in response both to nodes’ requests for communication bandwidth and nodes’ reports
of the channel qualities in their individual locations. Implementing this functionality from
scratch, while possible, may prove time-consuming and it may be more feasible to employ a
pre-certified ISA100.11a Network Manager. This, however, comes with a caveat:
ISA100.11a is designed as a complete networking solution for high-reliability industrial
process monitoring and control. As a result, an ISA100.11a-compliant Network Manager
functions on all levels (PHY through APP) of the OSI model. To achieve the PHY- and
MAC-sublayer behavior specified in this Recommended Practice, the use of a complete
ISA100.11a stack configured so that behavior at layers above the MAC sublayer is either
disabled or transparent to the user is advised. Specifically, the following configuration is
recommended:
a) All nodes, except for the network gateway, should be configured as non-routing
devices.
b) APP layer tunneling should be used to bypass the object-oriented APP layer scheme
recommended by ISA100.11a.
Configuration a) results in a star network topology, giving the single-hop behavior mandated
in this recommended practice. It reduces functionality at each of the upper Data Link and
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NWK layer to a pass-through, since the upper Data Link layer is responsible for multi-hop
routing within an ISA100.11a mesh network and the NWK layer is responsible for routing
outside of the gateway on the backbone network (a recommendation for which is not covered
in this document). Configuration b) reduces functionality at each of the Transport and APP
layers to a pass-through as well.
It is worth noting that over-the-air transmissions must be secured in an ISA100.11a network.
While security is optional in the 802.15.4 PHY/MAC recommendation, some level of
security is required in the ISA100.11a PHY/MAC recommendation implicitly through the
use of an ISA100.11a stack configured as directed above. A Security Manager entity joins
the Network Manager in a proper ISA100.11a implementation, and its inclusion is nonoptional. Messages are encrypted on both a hop-by-hop and end-to-end basis, and
distribution and maintenance of encryption keys is handled automatically by the Security
Manager.
As such, this Recommended Practice covers secure, single-hop communications. Should a
user wish to extend this functionality to multi-hop communication, configuration a) can of
course be ignored, but such functionality is outside the scope of the current recommended
practice.
It is also worth cautioning the user that ISA100.11a is a relatively resource-heavy protocol
with regards to computational complexity at the Network Manager. Network formation will
generally take longer compared to the 802.15.4 PHY/MAC recommendation, and support for
node mobility will be more limited. The same caveat applies to administrative messages to
the nodes from the Network Manager (and vice versa). A greater percentage of available
bandwidth will be used to maintain the ISA100.11a network to achieve more efficient use of
the remaining bandwidth in contention-based environments. Thus the current Recommended
Practice can be expected to work quite well in an environment in which contention for
bandwidth from other systems and interference effects are significantly present but not well
modeled. Conversely, when the available spectrum is well understood over time and
carefully managed, the current Recommended Practice may not be well suited.
C2
C2.1
APPLICATION PROFILES
OVERVIEW
An application profile is an explicit listing of the configuration settings of a typical
implementation that may be suitable for multiple use cases or applications. Table C-1 is a
quick-look table, which lists the most common application profiles targeted by the two
recommendations specified in this document. It should be noted that all of these application
profiles are based on a star network topology in which the individual nodes in the network all
communicate directly with a central gateway node that aggregates data, disseminates
commands, or both. Both the 802.15.4 standard, which is specified in 3.2.1 and the
ISA100.11a standard, which is specified in 3.2.2, are well suited for applications based on
such a topology and can be expected to work well for both periodic, fixed-length, block data
transfer as well as aperiodic, variable-length, bursty data transfer.
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Table C-1: Application Profile Quick Look-Up Table
List of application profiles falling under the recommended practice
1. Single-hop periodic data aggregation
2. Single-hop triggered (event-driven) data aggregation
3. Single-hop, latency tolerant command and control or command-driven data
aggregation (polling)
Table C-2 presents a set of use-cases that may benefit from using low data-rate wireless
communications.
Table C-2: Quick-Look Table for Scenarios That Can Utilize Low Data-Rate
Wireless Communications
Use-case
Typical examples
Assembly, Integration and Testing (AIT) /
Ground Support Equipment (GSE) /
Developmental Flight Instrumentation (DFI)
activities
Thermal chamber testing, vibration testing,
data bus monitoring…
Spacecraft onboard health monitoring
Temperature and radiation level monitoring,
impact detection…
Scalability / extensibility / retro-fit of
instrumentation capabilities
Instrument replacement, adding capability to
existing vehicles…
Habitat environmental monitoring and control
Temperature, humidity, pressure
monitoring…
Crew (physiological) monitoring
Heartbeat, temperature, location…
Scientific monitoring and control
Periodic observation of experimental
variables…
Intra-spacecraft robotic activities
low data-rate positioning telemetry, health
data…
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C2.2
SINGLE-HOP PERIODIC DATA AGGREGATION
The single-hop periodic data-aggregation profile covers the most common implementation of
a wireless sensor network, one that consists of a central data sink (i.e., a gateway or network
coordinator) and a number of child nodes that perform periodic data acquisition. The network
is configured in a star topology, with each child node having a direct link to the coordinator.
Typically, a child node wakes up from a very low-power (sleep) mode on a predetermined
periodic schedule, executes a data acquisition task, formats the acquired data, transmits a data
packet to the network coordinator, and then goes back into sleep mode. Alternatively, the
acquisition node may sample data during each wake cycle but only transmit data to the
coordinator when a full packet’s worth of data has been accumulated. The coordinator node,
which either never sleeps or sleeps only infrequently, aggregates the data from all of the child
nodes and relays it over a backbone network to user applications that consume the data.
Generally, the duty cycle of the child nodes is quite low, with data acquired at rates from one
observation per second down to one observation every several minutes and children often
spending 99 percent or more of their lifetimes in sleep mode. For this profile, the data
payload transmitted in each packet is generally small and fixed in size.
Vehicle ground test applications require flexibility in the implementation of the tests and the
location and orientation of the nodes and antennas. Hence, it is often the case that all nodes
will have omnidirectional antennas rather than directional higher-gain antennas.
The RF transmit power is a very application-specific parameter and heavily depends on the
operational environment and on EMI/EMC constraints. Some spacecraft will not allow
transmission powers higher than perhaps -15 dBm, while others may permit powers up to 10
dBm. In contrast, for other applications such as structural testing of small components in a
laboratory thermal-vacuum chamber, relaxed transmit power constraints are often seen. The
permissible transmit power is thus one of the first parameters/constraints to be identified
before setting up a wireless sensor network.
The number of acquisition nodes in the wireless network is also very application-dependent.
In a typical laboratory testing activity, a few nodes, each with several sensors, may well
prove to be enough for the task at hand. Spacecraft testing and monitoring on the other hand
may require the utilization of hundreds of wireless nodes.
Table C-3 summarizes the high-level implementation parameters and operational
configurations for the periodic data aggregation application profile.
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Table C-3: Typical Operating Parameters for the Single-Hop, Periodic Data
Aggregation Application Profile
Implementation parameter /
operational configuration
C2.3
Typical value
Topology
Star
Antenna type
Typically omnidirectional
Transmit power
Typically -15 dBm to +10 dBm
Typical number of nodes
10 – 100
Antenna Polarization (master/slave)
Linear/linear; circular/linear
Spectrum/Channel utilization
Per IEEE 802.15.4 specifications;
spectrum and channel management
Typical communication range
0 – 10 m
Typical transmit periodicity
Seconds to minutes
Expected battery life
Months to years
Typical receiver periodicity
Low
Latency constraints
Typically relaxed
Routing
None
Data payload characteristics
Periodic, fixed-length, uniform rate
SINGLE-HOP TRIGGERED EVENT-DRIVEN DATA ACQUISITION
The single-hop triggered-event-driven data-acquisition profile covers an implementation of a
wireless sensor network that consists of a central data sink and a number of child nodes that
perform non-periodic data acquisition. The network is configured in a star topology, with
each child node having a direct link to the coordinator. For this profile, however, a child node
wakes up to acquire data only when triggered by the occurrence of some local event rather
than on a predetermined periodic schedule. The triggering event is sensed by the child node
using a low-power circuit that remains active even in sleep mode. When data collection is
triggered, the acquisition node collects some amount of data, which may be either
predetermined or based on the length or intensity of the triggering event. The collected data
may be transmitted back to the sink in raw form or may be processed locally to reduce the
data in some fashion. In either case, the resulting data payload is formatted and transmitted
back to the sink via a single packet or subdivided into several sequential packets, as
necessary. The coordinator node, which either never sleeps or sleeps only infrequently,
aggregates the data from all of the child nodes and relays it over a backbone network to user
applications that consume the data. For this profile, the duty cycle of the child nodes is
obviously determined by the frequency of triggering events, but is generally extremely low.
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General considerations regarding antenna configuration, power level, and network size are
identical to those discussed in table C-3. Table C-4 summarizes the high-level
implementation parameters and operational configurations for the event-driven data
aggregation application profile.
Table C-4: Typical Operating Parameters for the Single-Hop Triggered, EventDriven Data Acquisition Application Profile
Implementation parameter /
operational configuration
C2.4
Typical value
Topology
Star
Antenna type
Typically omnidirectional
Transmit power
Typically -15 dBm to +10 dBm
Typical number of nodes
10 – 100
Antenna Polarization (master/slave)
Linear/linear; circular/linear
Spectrum/Channel utilization
Per IEEE 802.15.4 specifications;
spectrum and channel management
Typical communication range
0 – 10 m
Typical transmit periodicity
Event driven
Expected battery life
Months to years
Typical receiver periodicity
Low, depends on beacon and
acknowledgement mode
Latency constraints
Typically relaxed
Routing
None
Data payload characteristics
Non-periodic, variable-length, bursty
SINGLE-HOP COMMAND AND CONTROL OR COMMAND-DRIVEN
DATA AGGREGATION
The single-hop command-and-control or command-driven data-aggregation profile again
covers an implementation of a wireless sensor network that consists of a central coordinator
and a number of child nodes. In this case, however, the child nodes may acquire data from a
sensor, control an actuator, or both. Further, in this profile, data may flow not only from the
child node to the coordinator in the form of telemetry or command status, but also from the
coordinator to the child node in the form of commands. The network is configured in a star
topology, with each child node having a direct, bi-directional link to the coordinator.
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For the command-driven data aggregation application, a child node wakes up on a periodic
schedule and communicates with the coordinator for a possible command to acquire data. If
there is no command waiting, the node goes back into sleep mode. If there is a data
acquisition command waiting, the node decodes the command, acquires and formats the
requested amount of data, transmits the data back to the coordinator in as many packets as
necessary, and goes back into sleep mode. For the command and control application, the
child node wakes up on a periodic schedule and polls the coordinator for a possible command
to change an actuator setting. If there is no command waiting, the node goes back into sleep
mode. If there is an actuation command waiting, the node retrieves the command, decodes it,
activates an appropriate control signal for the actuator, optionally transmits a command status
to the coordinator (e.g., success/failure), and goes back into sleep mode. One could again
envision such an operation being conducted in conjunction with the periodic or eventtriggered transmissions in C2.2 and C2.3. Should a control algorithm interfacing with the
gateway decide a local actuation (e.g., turning on a heater or a fan) is necessary based on
measured data (e.g., a temperature reading), a command for that actuation would be sent to
the node which measured the data and is capable of actuating the control device.
For either application, the coordinator aggregates the data from all of the child nodes (either
telemetry or command status data) and relays it over a backbone network to user applications
that consume the data. The coordinator once again sleeps only infrequently. The duty cycle
of the child nodes is command-driven, but is generally extremely low.
General considerations regarding antenna configuration, power level, and network size are
again identical to those discussed in C2.2. Table C-5 summarizes the high-level
implementation parameters and operational configurations for both the command and control
and command-driven data aggregation application profiles.
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Table C-5: Typical Operating Parameters for the Single-Hop Command and Control
Application Profile
Implementation parameter /
operational configuration
Typical value
Topology
Star
Antenna type
Typically omnidirectional
Transmit power
Typically -15 dBm to +10 dBm
Typical number of nodes
10 – 100
Antenna Polarization (master/slave)
Linear/linear; circular/linear
Spectrum/Channel utilization
Per IEEE 802.15.4 specifications;
spectrum and channel management
Typical communication range
0 – 10 m
Typical transmit periodicity
Command-driven
Expected battery life
Months to years
Typical receiver periodicity
Low, depends on beacon and
acknowledgement mode
Latency constraints
Typically relaxed
Routing
None
Data payload characteristics
A-periodic, variable-length, bursty
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ANNEX D
JUSTIFICATIONS FOR THE 2.4 GHZ BAND PREFERENCE
(INFORMATIVE)
Standard 802.15.4 allows for operation at one frequency in the 868 MHz band (license-free
in Europe), ten frequencies in the 900-915 MHz band (license-free in the United States) and
sixteen frequencies in the 2.4-2.485 GHz band (license-free world-wide). Of these, the 2.4
GHz band was chosen for the following reasons.
Outside the United States, operation between 900 and 915MHz requires a license, and in
Europe systems operating in this band must compete with a radar band, so the license is
generally only available on an ‘at risk’ basis. This implies that the operator cannot restrict the
operation of an interfering system but can be shut down if it interferes with anyone else who
is licensed in that band. This incurs a risk to guaranteed operation.
Antennas for lower-frequency radiation must be larger than antennas for higher-frequency
radiation in order to achieve the same efficiency and gain. Hence, antennas for
communication nodes operating in the UHF bands (868 MHz and 900-915 MHz) will
generally be much larger than antennas for nodes operating in the 2.4 GHz band (see
reference [F3]).
The UHF wavelength is approximately 0.3 meters, which is of the same order as the size of
many spacecraft cavities. In such environments, UHF propagation is likely to be influenced
by resonant mechanisms. The 2.4 GHz wavelength is approximately 12.5 cm, so multipleantenna techniques can be readily utilized, even by small devices, to provide spatial diversity
and/or multiplexing gain in reverberant environments (see reference [F4]).
Because of the international acceptance of other 2.4 GHz systems such as 802.11b/g/n, radios
and antennas for this band are readily available commercially. Radios for 868-915 MHz are
less common. Additionally, with more frequencies available in the 2.4 GHz band, there is
more opportunity for selection to avoid co-channel or adjacent channel interference.
Regional Constraints
Unlicensed operation of wireless networks is in bands designated by the ITU, but governed
by national and international standards. At the top level, band availability is by ITU Region:
Region 1: Europe, Africa, the former Soviet Union, Mongolia, and the Middle East west of
the Arabian Gulf including Iraq.
Region 2: The Americas, Greenland, and some of the Eastern Pacific Islands.
Region 3: Most of Oceania, and Asia outside the former Soviet Union, with the exception of
those areas of the Middle East designated in Region 1.
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Under ITU regulations, the 900-928MHz band is not to be used outside Region 2, especially
in areas that use the GSM 900 band, with the exception of Australia and Israel.
In the United States, the ISM bands are described by Code of Federal Regulations
(CFR) Title 47 Part 18, and wireless LAN and PAN are governed by Part 15 Subpart 247.
Canadian regulation is Industry Canada regulations, with the basic regulations for licenseexempt operation covered by Radio Standards Specification (RSS) General Requirements
and Information for the Certification of Radio Apparatus (RSS-Gen), RSS-210 Licenseexempt Radio Apparatus (All Frequency Bands): Category I Equipment, and explicit
regulations in RSS-210 Annex 8. In addition, Health Canada Safety Code 6 sets radio
frequency emission exposure limits. Communications standards in this band for the US and
Canada, operating in the region close to the US-Canada border, are coordinated under Treaty
Series 1962 No. 15 - Coordination and Use of Radio Frequencies Arrangement D (1965).
In Europe the over-arching definition is by the European Telecommunications Standards
Institute (ETSI), but this is subject to acceptance and ratification by local regulatory authorities.
This is normally a matter of formality only. The applicable standard is EN 300 328.
Japanese regulation is governed by standard ARIB-STD-T66. The official version is in
Japanese, but the Association of Radio Industries and Businesses (ARIB) provides an
English overview on their site www.arib.or.jp. This second-generation standard governs only
the use of the 2400-2483.5 MHz band. The first generation allowed use only in the 24712497 MHz band.
Table D-1: Power Regulations
Band
US/Canada
Europe
Japan
2400 – 2483.5
MHz
Freely available.
1W maximum.
Freely available, 100mW
maximum.
Freely available,
10mW / MHz
maximum.
868MHz
No.
Available, 1 channel of
operation in 802.15.4, 868868.6 MHz, 25mW
maximum, duty cycle less
than 1% in any one hour time
period.
No.
902-928 MHz
Freely available,
unlicensed, 1W
maximum.
Not available except with a
license and on a noninterfering basis. Clashes
with GSM900.
No.
This annex summarizes the national regulations for unlicensed operation of low-power lowrate data networks. These are the salient points; there is much more regulation of ancillary
issues such as out-of-band emissions, and should the system designer seek to source or design a
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radio, rather than using one which is commercially available and states compliance to the
regulations, then the source regulations will have to be consulted. Although not all authorities
have been consulted, the European regulations have been largely adopted in ITU Region 1, the
FCC/RSS Regulations in ITU Region 2, and the Japanese regulation in ITU Region 3.
As can be seen from the foregoing, the 2400-2483.5 MHz band is the only one, applicable to
802.15.4, that is universally adopted.
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ANNEX E
ABBREVIATIONS AND ACRONYMS
(INFORMATIVE)
AIT
assembly, integration and testing
APP
Application (Layer)
ARIB
Association of Radio Industries and Businesses
CA
collision avoidance
CAP
contention access period
CCA
clear channel assessment
CCSDS
Consultative Committee for Space Data Systems
CFP
contention free period
CFR
Code of Federal Regulations
CSMA
carrier-sense multiple access
CSMA-CA
carrier-sense multiple access with collision avoidance
DFI
developmental flight instrumentation
DSSS
direct-sequence spread spectrum
EMC
electromagnetic compatibility
EMI
electromagnetic interference
ETSI
European Telecommunications Standards Institute
FCC
Federal Communications Commission
GSE
ground support equipment
GSM
Global System for Mobile Communications (originally Groupe Spécial Mobile)
GTS
guaranteed time slots
IEEE
Institute of Electrical and Electronics Engineers
IP
Internet Protocol
ISM
industrial, scientific, and medical
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ISO
International Organization for Standardization
ITU
International Telecommunication Union
LAN
local area network
MAC
media access control
NWK
Network (Layer)
OSI
Open System Interconnection
PAN
personal area network
PHY
Physical (Layer)
QoS
quality of service
RF
radio frequency
TDMA
time-division multiple access
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ANNEX F
INFORMATIVE REFERENCES
(INFORMATIVE)
[F1] Information Technology—Open Systems Interconnection—Basic Reference Model: The
Basic Model. International Standard, ISO/IEC 7498-1:1994. 2nd ed. Geneva: ISO,
1994.
[F2] Karl Holger and Andreas Willig. Protocols and Architectures for Wireless Sensor
Networks. West Sussex, England: Wiley-Interscience, 2007.
[F3] Constantine Balanis. Antenna Theory: Analysis and Design. 3rd ed. Hoboken, N.J.:
Wiley-Interscience, 2005.
[F4] John Proakis and Masoud Salehi. Digital Communications. 5th ed. Boston: McGrawHill, 2008.
[F5] Space Data Link Security Concept of Operation. Draft Report Concerning Space Data
System Standards, CCSDS 350.5-G-0. Draft Green Book. Issue 0. Washington, D.C.:
CCSDS, forthcoming.
[F6] Naveen Sastry and David Wagner. “Security Considerations for IEEE 802.15.4
Networks.” In WiSe ’04 Proceedings of the 3rd ACM Workshop on Wireless Security
(October 1, 2004, Philadelphia), 32-42. New York: ACM, 2004.
[F7] IEEE Standard for Local and Metropolitan Area Networks—Part 15.4: Low-Rate
Wireless Personal Area Networks (LR-WPANs)—Amendment 1: MAC Sublayer. IEEE
Std 802.15.4e™-2012. New York: IEEE, 2012.
[F8] Raymond Wagner and Richard Barton. “Performance Comparison of Wireless Sensor
Network Standard Protocols in an Aerospace Environment: ISA100.11a and ZigBee
Pro.” In Proceedings of the IEEE Aerospace Conference, 2012 (3-10 March 2012 ), 1–
14. New York: IEEE, 2012.
[F9] Stig Petersen and Simon Carlsen. “WirelessHART vs. ISA100.11a: The Format War
Hits the Factory Floor.” IEEE Industrial Electronics Magazine 5, no. 4 (2011): 23–34.
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